1. Field of the Invention
The present invention relates to an implantable heart monitoring and stimulating device with which it is possible to stimulate both the ventricles of a heart, i.e. a bi-ventricular pacer. The invention also relates to a system including such a device and to a cardiac stimulating method.
2. Description of the Prior Art
Several different implantable devices for monitoring and stimulating a heart are known. The devices normally are able to sense the electrical activity of the heart and to deliver stimulation pulses to the heart. Some implantable devices are able to sense, and deliver stimulation pulses to, both the left and right ventricles of the heart.
Devices that are able to deliver stimulation pulses to both the left and right ventricle also are called bi-ventricular pacers. Such devices can be used to treat patients who suffer from different severe cardiac problems, e.g. patients suffering from congestive heart failure (CHF). CHF is defined generally as the inability of the heart to deliver a sufficient amount of blood to the body. CHF can have different causes. For example, it can be caused by a left bundle branch block (LBBB) or a right bundle branch block (RBBB). By using bi-ventricular pacing, the contraction of the ventricles can be controlled in order to improve the ability of the heart to pump blood. The stimulation pulses to the two ventricles can be delivered simultaneously but it is also known to deliver the stimulation pulses to the two ventricles with a short time delay between them in order to optimize the pumping performance of the heart.
U.S. Pat. No. 5,720,768 describes different possible electrode positions in order to stimulate or sense the different chambers of the heart.
U.S. Pat. No. 6,070,100 describes that electrodes may be positioned to sense and stimulate both the left atrium and the right atrium as well as the left and the right ventricles.
In connection with implantable heart stimulating devices, it is thus known to sense different signals with the help of the implanted electrodes and to control the heart stimulating device in response to the sensed signals. It is known, for example, to inhibit the delivery of a stimulating pulse if a natural, intrinsic, heart activity is detected. One difficulty in this context is to identify the signals that the device senses. Signals may originate from different intrinsic events in different parts of the heart. Signals may also originate from the heart stimulating device itself, i.e. from pulses delivered by different implanted electrodes. Signals even may have external causes, for example an external electromagnetic alternating field to which the person with the implanted device is exposed.
One kind of detected signal is a so-called far field signal. This is a signal that is detected by an implanted electrode, but which originates from some other part of the heart than that which it is intended to sense with the electrode in question. This phenomenon is known in connection with pacers arranged to sense or stimulate both the right atrium and the right ventricle. It is for example known that an electrode positioned in the right atrium may sense an R-wave, i.e. a QRS complex, when this electrode actually should sense a P-wave. The sensed R-wave is thus in this case a far field signal. Different ways to avoid this problem have been suggested in connection with pacers arranged to sense or pace the right atrium and the right ventricle.
In connection with bi-ventricular pacers, or four chamber pacers, different kinds of problems concerning far field detection may occur than those known in connection with pacers arranged to sense or pace only the right atrium and the right ventricle.
PCT Application WO 02/45797 describes systems and methods for distinguishing a valid sensed signal from an invalid signal, such as a myopotential. When sensing a left ventricular signal, the system starts an “intrinsic inhibition window”. If and only if a right ventricular signal is sensed during this window, the sensed left ventricular signal is considered to be a valid sensed signal.